AH Bio 3.2

what ensures validity?

control of dependant variables

what is reliability?

consistent values in repeats and independent replicates

what is accuracy?

how close data is to the true value

what is precision?

how close data values are to one another

what is a pilot study?

a small scale investigation of a planned research project

what are 3 advantages of a pilot study?

helps researchers to refine a research question, figure to what methods to use, estimate how much time and resources will be required for the experiment

what is an independent variable?

the one that is changed

What is a dependent variable?

the one that is measured

what is a confounding variable?

one other than the independent variable that may affect the dependent variable

what are two advantages of simple experiment designs?

variables are tightly controlled, results are easy to analyse and interperate

what are two disadvantages of simple experimental design?

difficult to extrapolate results to whole organisms or environments, not suitable for testing complex hypotheses

what are two advantages of using multifactorial experimental design?

allows examination of complex interactions, results applicable to study environment or an organism

what are two disadvantages of using multifactorial experimental design?

more complex and time consuming, difficult to control all variables

what do observational studies study?

pre-existing groups but at the expense of being unable to control the independent variable

when do positive correlations occur?

when one variable increases as the other increases

when no negative correlations occur?

when one variable increases as the other decreases

what does correlation not mean?

causation

what can be used in cases where confounding variables cannot be easily controlled?

randomised block design

how does a randomised block design work?

the influence of any confounding variables is likely to be the same across the treatment and control groups

what are control results used for?

comparison with results of treatment groups

what is a negative control?

a group with no treatment

if the negative control group yields an unexpected response, what could this suggest?

there is an unknown confounding variable affecting the experiment

what is a positive control?

a treatment that is included to check that the system can detect a positive result when it occurs

what is a placebo?

a treatment without the presence of the independent variable that is being investigated

what is any change in the dependent variable caused by during the placebo effect?

the patients expectations

what is an in vivo study?

experimentation using a whole, living organism

What is an in vitro study?

experimentation in a controlled environment outside of a living organism

what are two advantages of an in vivo study?

provides data for effects on whole organisms, allows study of complex interactions

what are two disadvantages of an in vivo study?

expensive and time consuming, ethical and legislative concerns

what are two advantages of an in vitro study?

simpler and less expensive, easier to control confounding variables

what are two disadvantages of an in vitro study?

difficult to extend results to whole organisms or different species, difficult to model complex interactions

where it is impractical to measure every individual in a population or ecosystem, what is selected?

a representative sample of the population

what may be lost when a larger sample size is used?

correlation

what should a representative sample share with the population as a whole?

the same mean and degree of variation

what is normal distribution?

known as a bell curve, the central value is the mean, median and mode

What is a skewed distribution?

a representation of scores that lack symmetry around their average value

what is random sampling?

every member of the population has an equal chance of being selected

what is an advantage of random sampling?

it reduces bias

what is a disadvantage of random sampling?

it can result in poor representation of the main population

what is systematic sampling?

members of a population are selected at regular intervals

what is an advantage of systematic sampling?

it provides a more representative sample of a population

what s a disadvantage of systematic sampling?

it may be biased because members no not all have an equal chance of being selected

what is stratified sampling?

the population is divided into categories that are then sampled proportionally

what is an advantage of stratified sampling?

it gives a highly representative sample of the population

what is a disadvantage of stratified sampling?

the proportions of each group within the population must be known

what could variation in experimental results by due to?

the reliability of methods

how can the reliability of measuring instruments or procedures be determined?

repeated measurements of an individual datum point

what can be determined by measuring a sample of individuals from the population?

the natural variation in the biological material

what helps to produce a more representative result of a sample?

using a larger sample size

When can results be considered reliable?

when they can be achieved consistantly

when does correlation exist?

when there is a relationship between two variables

When does causation exist?

if the changes in the values of the independent variable are known to cause changes to the value of the dependent variable